.\" RCSid "$Id: ra_xyze.1,v 1.6 2010/12/16 21:34:41 greg Exp $"
.TH RA_XYZE 1 5/30/96 RADIANCE
.SH NAME
ra_xyze - convert between RADIANCE RGBE and XYZE formats
.SH SYNOPSIS
.B ra_xyze
[
.B \-r
][
.B "\-e exposure"
][
.B \-o
][
.B \-c
|
.B \-u
][
.B "\-p xr yr xg yg xb yb xw yw"
]
[
.B input
[
.B output
]
]
.SH DESCRIPTION
.I Ra_xyze
converts between RADIANCE RGBE (red,green,blue,exponent) and XYZE
(CIE X,Y,Z,exponent) formats.
The
.I \-e
option specifies an exposure compensation, which may be given as
a decimal multiplier or in f-stops (powers of two).
The
.I \-o
option may be used to specify original units, to which the exposure
compensation is applied.
Otherwise, the multiplier is in addition to any previous exposure adjustment.
By default,
.I ra_xyze
produces a flat XYZE RADIANCE picture file from any type of RADIANCE
input picture.
To override these defaults, the
.I \-c
option may be used to specify run-length encoded output,
or the
.I \-u
option may be used to specify a flat output.
.PP
The
.I \-r
option causes
.I ra_xyze
to produce a run-length encoded RGBE file instead, unless
.I \-u
is given, also, when it will produce a flat RGBE file.
The
.I \-p
option may be used to override the standard RADIANCE RGB primary
colors to tailor the image for a particular output device or
representation.
The eight floating-point arguments to this option are the 1931
CIE (x,y) chromaticity coordinates of the three RGB primaries
plus the white point, in that order.
The new primaries will be recorded in the header of the output file,
so that the original information may be fully recovered later.
It is not necessary that the input file be in XYZE format.
Th
.I \-r
option may therefore be used to convert from one RGB primary
representation to another using the
.I \-p
option.
.PP
If the output file is missing, the standard output is used.
If the input file is missing as well, the standard input is used.
.SH NOTES
The CIE standard used is the 1931 2-degree observer, and the
correct output representation relies on the original RADIANCE
input description being defined properly in terms of the standard
RADIANCE RGB primaries, whose CIE (x,y) chromaticity values are
defined in the header file in src/common/color.h.
In this same file is a standard for the luminous efficacy of white
light (WHTEFFICACY), which is used as a conversion between lumens
and watts throughout RADIANCE.
This same factor is applied by
.I ra_xyze
when converting between the radiometric units of the RGBE format
and the photometric units of the XYZE format.
The purpose of this factor is to ensure that the Y component of
the CIE representation is luminance in units of candelas/meter^2.
.PP
Most of the RADIANCE picture filters should work uniformly on either
RGBE or XYZE files, so it is not necessary to convert back to RGBE
format except for conversion or display, in which case the correct
primaries for the chosen output device should be specified with the
.I \-p
option if they are known.
.SH EXAMPLES
To convert RGBE output from
.I rpict(1)
into run-length encoded XYZE format:
.IP "" .2i
rpict [options] scene.oct | ra_xyze \-c > scene_xyz.hdr
.PP
To prepare a RADIANCE picture for display on a calibrated NTSC monitor:
.IP "" .2i
ra_xyze \-r \-p .670 .330 .210 .710 .140 .080 .333 .333 stand.hdr ntsc.hdr
.SH AUTHOR
Greg Ward
.SH BUGS
Any color correction applied to the original image is not removed
or translated by
.I ra_xyze,
and it may result in color shifts in the output.
If color preservation is important and the correction is unwanted,
it is best to remove it with
.I pfilt(1)
using the
.I \-er,
.I \-eg
and
.I \-eb
options first.
(Simply look at the header and apply the reciprocal primaries of all
COLORCORR= lines multiplied together.)
Better still, get the picture before color correction is applied.
.SH "SEE ALSO"
pfilt(1), pvalue(1), ra_rgbe(1), rpict(1)
